B. hominis mitochondria have no lactic dehydrogenase, isocitrate, dehydrogenase, glycerol dehydrogenase, cytochrome oxidase, glutamate dehydrogenase, dihydrolipoemide, dehydrogenase, alpha keto-glutarate dehydrogenase, or pyruvate dehydrogenase enzymatic activity. B. hominis has an absolute requirement for cholesterol. The main acid products from glucose are acetic, propionic, succinic, lactic, and isovaleric acids. Spectrographic analysis for cytochromes and flavoprotein was negative. Thus, these mitochondria lack enzymes, as well as cytochromes that are normally present in mitochondria. It was discovered that humans have a strong serological (IgG) response to Blastocystis hominis infections. Progress: Ultrastructure of B. hominis (major features) is on a solid footing now. There is much to be done concerning the function of the central body and its role in schizogony. There are also questions to be answered re ameba-form ultrastructure, but these will wait for someone else's input. I am presently studying a species of Blastocystis not hominis, from the trumpeter swan. This will probably come to publication within the next year. We have now titered fourteen human sera from humans with B. hominis infection. All had an IFA titer of 1:400 to 1:1000. Sixty blood bank sera were IFA negative for B. hominis antibodies.